1. Field of the Invention
The present invention relates to a multistage thermoelectric cooling device including a plurality of stacked cooling units each of which is interposed between two vertically adjacent substrates so as to cool a substance on the most upper substrate, and in particular to a soldering structure between an end of a thermoelectric element and an electrode at which an amount of heat is evolved or absorbed by the Peltier effect.
2. Description of the Related Art
A known conventional multistage thermoelectric cooling device is disclosed in Japanese patent Laid-open Print No. Hei 2 (1990)-10781. This conventional multistage thermoelectric cooling device includes a plurality of cooling assemblies, each of which provides heat absorption at one side thereof by the Peltier effect, which are stacked in the vertical direction such that each cooling unit is interposed between two adjacent substrates so that the most upper substrate is brought into the most cooled condition. For providing the foregoing heat absorption, an electrode which constitutes a cold junction of two adjacent different type thermoelectric elements of the lower side cooling unit is adhered to a lower surface of its upper side substrate. The electrode is soldered with ends of the thermoelectric elements. Such soldering in the upper side cooling unit is established after completion of the soldering in the next lower cooling unit.
However, the heat used for soldering in the upper cooling unit which is mounted on the upper side substrate of the next lower cooling unit is transferred thereto when the upper side substrate is thin, resulting in that sometimes the soldering in the next lower cooling unit may become damaged or remelted. Thus, in the next lower cooling unit the connection strength becomes weak between the electrode and each of the thermoelectric elements and an unexpected offset of the former from the latter occurs. This means the designed performance and reliability of the multistage thermoelectric cooling device not be attained.